Amgen's biosimilar Humira product – currently known as ABP 501 – will be assessed by an FDA advisory committee this week. With the agency having already approved two biosimilar products, including authorisation of its first biosimilar monoclonal antibody earlier this year, expectations for a regulatory hat-trick were already high; FDA briefing documents released on Friday appear to make approval of ABP501 largely a formality.

Most importantly, the FDA is satisfied with the data submitted by Amgen which "support a demonstration that ABP 501 is highly similar to US-licensed Humira." In fact, expectations may have been exceeded with the agency noting data are supportive of a scenario whereby "non-treatment naïve patients may undergo a single transition to ABP 501 from Humira."

This is the type of phraseology that AbbVie and other manufacturers of originator biologics don't want to hear. Furthermore, this sentiment shows just how quickly the FDA has become comfortable in approving biosimilars and provides further evidence the agency may tacitly support patient switching prior to publishing long awaited guidance on interchangeability.

In this sense, the briefing documents for ABP 501 can be viewed as a continuation of the FDA's increasingly confident stance towards biosimilarity, which was very much in evidence during the AdCom panel convened in February to discuss Celltrion's biosimilar Remicade product CT-P13. In that meeting, the agency was "far more emphatic in their support of the product," (in comparison to 2015's AdCom for Novartis' Zarxio) and "more active in clarifying why it had reached its conclusions," Gillian Woollett – FDA practice lead at Avalere – told FirstWord at the time.

Another important comparison is that the FDA will utilise similar questioning next week to that which was used in February, by asking panellists to partake in a singular vote for approval across all indications Amgen is seeking clearance for; approval for all indications by extrapolation now looks almost certain to happen, notes FirstWord's Duncan Emerton, who authors The Biosimilar Index.

If a key takeaway from February's AdCom was the FDA's success in educating and convincing panel members of the fundamental difference between the concept of biosimilarity and the premise of originator drugs, that meeting also provided confirmation that Celltrion had submitted data from a single switch study – from Remicade to CT-P13 – at the behest of the regulator. Reference to this data did not make it into labelling for the biosimilar, but the agency's reference to ABP 501 potentially being used as an alternative therapy to Humira in non-treatment naïve patients is "very significant," says Emerton; it also holds clear commercial implications.

AbbVie does appear to have time on its side. Assuming ABP 501 gains approval by its PDUFA date of September 25 and assuming a 180-day notice period, this would allow Amgen to launch its biosimilar 'at risk' in March of next year. Analysts expect Amgen to wait at least until ongoing litigation between Coherus Biosciences and AbbVie is resolved, while AbbVie is confident of intellectual property protection for Humira until 2022.

With Humira generating global sales of $14 billion last year, there are no shortage of biosimilar competitors in the pipeline; 11, according to FirstWord's Biosimilar Index, of which eight are currently in Phase III studies. Amgen may be the first to secure approval, but first-to-market status is not guaranteed. In the meantime, however, biosimilar manufacturers – not to mention eager US payers – can take heart from the FDA's increasingly progressive stance.